What do the terms diploid and haploid mean? Give an example of a diploid cell and a haploid cell.

- Diploid means a cell has the full amount of DNA e.g. all cells of the body except gametes
- Haploid means a cell has half the amount of DNA e.g. gametes (sperm and egg)

Diploid means a cell has the full amount of DNA e.g. all cells of the body except gametes

Haploid means a cell has half the amount of DNA e.g. gametes (sperm and egg)

There are four characteristic functions of a cell:
1. Cell metabolism and energy use
2. Synthesis of molecules
3. Reproduction and inheritance
4. Communication

Secondary structure of proteins:
The secondary structure of proteins results from hydrogen bonds (red dotted lines) that join the individual amino acids from the primary structure to form a pleated (folded) sheet or a helix (coil)

Collagen fibril (found in connective tissue) is made up of three polypeptide chains twisted around each other (Figure 11.4) and is called a fibrous protein.

DNA carries the recipe for each protein. A gene is a segment of DNA that carries the instructions that specify the structure of a specific protein. The production of a protein, using the information stored in DNA, is called gene expression. Gene expression can be divided into two parts:
1. Transcription
2. Translation

Both DNA and RNA consist of the basic building blocks called nucleotides

DNA is a double-stranded molecule and consists of two stands – the coding strand and the template strand

Chromatid:
• When a chromosome replicates ready for cell division, the two bits of replicated chromosomes that form are called chromatids.
• Each of these chromatids is called a chromosome again when they separate and move into the daughter cells.

Homologous pair:
• Chromosome pairs are called homologous pairs, each member of the pair is called a homologue.
• One homologue is derived from your mother and one from your father.
• Each chromosome in the pair codes for the same genes, so you have two versions of every gene, these are called alleles.

Cytokinesis
• The division of cell organelles and cytoplasm.
• Results in two identical daughter cells.

Unlike mitosis: the cell divides and pulls one of each pair of homologous chromosomes into each daughter cell (each chromosome still has two chromatids).

If a pathogen breaches the physical barriers of the body, our next line of defence is an immediate, but non-specific (innate) response such as inflammation.

Cell-mediated responses:

• Macrophages and other cells of the innate defences alert T cells that foreign antigens are present in the body.
• In your body you have specific small populations of T cells that recognise different types of antigens. When the antigen is recognised by the specific T cell, the T cell will directly attack the infected cells and release chemicals that further promote innate immune responses e.g. inflammation and phagocytosis.
• T cells also contribute to the activation of B cells (antibody mediated responses)
• A small population of T cells remain after the infection is cleared – memory T cells. The memory T cells means the next time that particular strep bacteria enters Tom’s body he will be able to fight it off faster.

Antibody-mediated responses:

• Once B cells are activated by the presence of the foreign antigen and with the help of T cells they differentiate into antibody releasing cells called plasma cells.
• Antibodies have many ways of eliminating the antigen. You don’t need to know all of them, but a few examples are:
- binding to the antigen to inactivate it
- binding to several antigens together to form a “clump” of antigens and make them in effective.
- when an antibody binds to an antigen, the complex is then often phagocytised by macrophages.
• Like T cells, a small population of memory B cells remain after the infection is cleared and will help Tom fight off the strep infection faster next time.